JP2006231563A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve deterioration in image quality, caused by misregistration of a dot, by sufficiently reducing the amount of the misregistration of the dot, recorded by a plurality of recording heads, along a sub-scanning direction. <P>SOLUTION: In a color printer, a printhead driving part 72 computes the correction amount of lead resist and that of skew along the main scanning direction with respect to printheads 32Y, 32M and 32C, so as to minimize the sum of squares of the amount of the misregistration, along the sub-scanning direction, of each dot, recorded on a photo conductor by LED arrays 80 of the printheads 32Y, 32M and 32C, with respect to each dot recorded on the photo conductor by an LED array 80 of a standard printhead 32K. After that, in the color printer, printhead driving part 72 changes the light-emitting timing of the LED arrays 80 of the printheads 32Y, 32M and 32C on the basis of the correction amount of lead resist, and changes the amount of the inclination of the other printheads 32Y, 32M and 32C with respect to the main-scanning direction on the basis of the correction amount of skew. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that records an image using a recording head for each color in which a plurality of output elements are arranged.

  Generally, a tandem type image forming apparatus records a color image on a recording medium by superimposing four color toner images of yellow (Y), magenta (M), cyan (C), and black (K). . In such an image forming apparatus, there is a recording head provided with a long print head for each color in which light emitting elements such as LEDs are arranged in the main scanning direction.

  When manufacturing such a long print head, it is ideal to manufacture the LEDs so that the LEDs are arranged in a straight line. There are cases where the position of the recorded dot in the sub-scanning direction deviates from the set value. Since the degree of misregistration varies from print head to print head, when recording a color image by overlaying multiple color images using the print head for each color as described above, the image of each color is at a predetermined position. A non-overlapping phenomenon (so-called “color misalignment” or “position misalignment”) occurs, causing image quality to deteriorate. Further, depending on the mounting state of the print head with respect to the image forming apparatus or the mechanical state of the image forming apparatus (for example, the inclination of the photosensitive member), skew is generated in the scanning lines recorded by each print head, It may cause misalignment.

  Regarding skew, after the print head is attached to the image forming apparatus, the positional deviation in the sub-scanning direction of the dots recorded by the light emitting elements near both ends of the print head is detected by the positional deviation detection sensor, and the dots near the both ends are detected. Conventionally, a method of correcting skew by rotating each print head so that the recording positions match for each color has been performed.

By the way, in an image forming apparatus that uses a plurality of LED image bars to superimpose a plurality of latent images developed in different colors to form an image, it corrects the misalignment of the LED image bars caused by the conicity of the photosensitive belt. As a way to do this, each bar is first aligned along the scan direction or Y-axis, then aligned along the process direction or X-axis, and a plurality of LED image bars are aligned in the scan direction and the process direction. After the initial alignment is performed, the method of performing the subsequent alignment by moving or rotating the bar according to the detection of the positional deviation signals of two reference images specified in advance is known. (For example, refer to Patent Document 1).
JP-A-5-345448

  However, in the above-described conventional method for correcting misregistration, the relative positions of the dots recorded by a plurality of print heads along the sub-scanning direction and the main scanning direction caused by manufacturing variations of each print head. Since the shift cannot be effectively corrected (reduced), a high-quality image cannot be recorded.

  In view of the above facts, an object of the present invention is to perform sub-scanning of dots recorded by a plurality of recording heads in an image forming apparatus that records an image using a recording head for each color in which a plurality of output elements are arranged. An object of the present invention is to provide an image forming apparatus in which the amount of misregistration along the direction is sufficiently small and image quality degradation caused by the misregistration of dots can be effectively improved.

  In order to achieve the above object, an image forming apparatus according to claim 1 of the present invention is provided with a plurality of recording heads having a plurality of output elements arranged in a line along the movement path of the image carrier, and in the sub-scanning direction. An image forming apparatus for forming an output image of a plurality of colors by superimposing a single color image formed by each recording head on the image carrier that moves to each of the image bearing members, and each output element in the predetermined recording head serving as a reference For each dot recorded in the image forming area of the image carrier along the sub-scanning direction of each dot recorded in the image forming area of the image carrier by each output element in the other recording head. The lead registration correction amount along the main scanning direction with respect to the other recording head and the main scanning with respect to the other recording head so that the respective positional deviation amounts are minimized. A first correction amount calculation means for calculating a skew correction amount for the direction, and an output timing of an output element in the other recording head is changed based on the read registration correction amount calculated by the first correction amount calculation means. And a lead correction correction unit for changing the inclination amount of the other recording head with respect to the main scanning direction based on the skew correction amount calculated by the first correction amount calculation unit. It is characterized by.

  In the image forming apparatus according to the first aspect, the first correction amount calculation unit is configured so that other output for each dot recorded in the image forming area of the image carrier by each output element in a predetermined recording head serving as a reference. Along the main scanning direction with respect to the other recording heads, the amount of positional deviation along the sub-scanning direction of each dot recorded in the image forming area of the image carrier by each output element in the recording head is minimized. The read resist correction amount and the skew correction amount in the main scanning direction for the other recording heads are calculated.

  At this time, when the width (image size) along the main scanning direction of the output image changes, the range in which the output elements used for forming a monochrome image in each recording head are arranged along the main scanning direction also changes. However, the first correction amount calculation means determines only the position of the dot formed by the output element corresponding to the image forming area of the image carrier among all the output elements in the recording head, and the read registration correction amount and the skew correction amount. Therefore, even if the image size along the main scanning direction of the output image changes, the optimum read registration correction amount and skew correction amount corresponding to the image size can always be calculated.

  Next, in the image forming apparatus according to the first aspect, the lead registration correction unit changes the light emission timing of the output element in the other recording head based on the lead registration correction amount calculated by the first correction amount calculation unit. The skew correction unit changes the amount of inclination with respect to the main scanning direction of the other recording heads based on the skew correction amount calculated by the first correction amount calculating unit, whereby each output in a predetermined recording head serving as a reference For each dot recorded on the image carrier by the element, an image is formed with the amount of positional deviation along the sub-scanning direction of each dot recorded on the image carrier by each output element in the other recording head. Can be minimized as the average of all of the multiple output elements used to make a given single color as a reference in the output image Able to not visually inconspicuous positional deviation in the main scanning direction of the other single-color image to the image (color misregistration) distributed along the main scanning direction.

  As a result, according to the image forming apparatus of the first aspect, for example, by the output element arranged at a part along the main scanning direction of the recording head, such as both ends and the center, along the main scanning direction of the recording head. Compared with the case where the read resist correction amount and the skew correction amount are set based on only the dot to be recorded, and the recording head is read resist corrected and skew corrected according to the read resist correction amount and the skew correction amount, Thus, it is possible to effectively improve the image quality degradation caused by the positional shift (color shift) along the sub-scanning direction of the other single-color image with respect to the predetermined single-color image.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein each image is recorded in an image forming area of the image carrier by each output element of the predetermined recording head serving as a reference. For each dot, the positional displacement amount along the main scanning direction of each dot recorded in the image forming area of the image carrier by each output element in the other recording head is minimized. A second correction amount calculating means for calculating a side registration correction amount along the main scanning direction with respect to another recording head; and the other correction amount based on the side registration correction amount calculated by the second correction amount calculating means. And a side resist correcting means for displacing the recording head along the main scanning direction.

  In the image forming apparatus according to the second aspect, the second correction amount calculation unit is configured so that each of the dots in the other recording heads corresponds to each dot recorded on the image carrier by each output element in the predetermined recording head serving as a reference. The side registration correction amount along the main scanning direction with respect to the other recording heads is calculated so that the positional deviation amount along the main scanning direction of each dot recorded on the image carrier by the output element is minimized. .

  At this time, when the width (image size) along the main scanning direction of the output image changes, the range in which the output elements used for forming a monochrome image in each recording head are arranged along the main scanning direction also changes. However, when the first correction amount calculation means calculates the side registration correction amount only for the positions of dots formed by the output elements corresponding to the image forming area of the image carrier among all the output elements in the recording head. Therefore, even if the image size along the main scanning direction of the output image changes, the optimum side registration correction amount according to the image size can always be calculated.

  Next, in the image forming apparatus according to claim 2, the side registration correction unit displaces another recording head along the main scanning direction based on the side registration correction amount calculated by the second correction amount calculation unit. Thus, in the main scanning direction of each dot recorded on the image carrier by each output element in the other recording head with respect to each dot recorded on the image carrier by each output element in the predetermined recording head as a reference The amount of misalignment along each other can be minimized as an average of all the plurality of output elements used to form the image, so that the main scanning direction of the other single-color image with respect to a predetermined single-color image serving as a reference in the output image Misalignment (color misregistration) along the main scanning direction can be dispersed and visually inconspicuous.

  As a result, according to the image forming apparatus of the second aspect, for example, the side registration correction amount is set based on only dots recorded by the output elements arranged at both ends of the recording head in the main scanning direction. Compared with the case where the recording head is subjected to side registration correction according to the registration correction amount, image quality deterioration caused by positional deviation (color deviation) along the main scanning direction of another single color image with respect to a predetermined single color image serving as a reference in the output image is reduced. It can be improved effectively.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the correction amount calculating means calculates a correction amount that minimizes a sum of squares of the respective displacement amounts. It is characterized by that.

  An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to any one of the first to third aspects, wherein the recording head is formed by all output elements provided in the recording head. First storage means for storing the relative positional relationship of the dots recorded on the carrier along the main scanning direction is provided, and the first correction amount calculation means is stored in the first storage means. Of all the output elements in the stored recording head, each dot recorded on the image carrier by each output element corresponding to the image forming area has a relative positional relationship along the main scanning direction. Based on this, the read resist correction amount and the skew correction amount for the other recording head are determined.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the second to fourth aspects, wherein the recording head is formed by all output elements provided in the recording head. A second storage unit that stores a relative positional relationship of each dot recorded on the carrier along the sub-scanning direction; and the second correction amount calculation unit includes the second storage unit. Among all the output elements in the recording head stored in the image, the relative positional relationship along the sub-scanning direction of each dot recorded on the image carrier by each output element corresponding to the image forming area The side registration correction amount for the other recording head is determined based on the above.

  According to a sixth aspect of the present invention, the image forming apparatus according to any one of the first to fifth aspects performs a correction operation when performing image formation of a size different from that at the previous image formation. It is characterized by performing.

  An image forming apparatus according to a seventh aspect of the present invention is the image forming apparatus according to any one of the first to sixth aspects, wherein the recording head has a light emitting element as an output element, and faces the recording head. And exposing the photoconductor provided by the light emitting element to record dots by electrophotography in an image forming area having a width corresponding to an output image along the main scanning direction in the image carrier. Features.

  As described above, according to the image forming apparatus of the present invention, in an image forming apparatus that records an image using a recording head for each color in which a plurality of output elements are arranged, dots recorded by the plurality of recording heads are recorded. By making the amount of positional deviation along the sub-scanning direction sufficiently small, it is possible to effectively improve the image quality degradation caused by the positional deviation of the dots.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be applied to an apparatus for forming a color image by arranging print heads of various colors in a tandem, such as an ink jet type or an electrophotographic color printer. Hereinafter, the present invention is applied to an electrophotographic color printer. A case where the present invention is applied to a printer will be described.

  FIG. 1 is a diagram showing an outline of a color printer according to the present embodiment. As shown in FIG. 1, in a color printer (hereinafter referred to as a printer) 10 as an image forming apparatus, toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are respectively continuous. Print sections 12Y, 12M, 12C, and 12K (hereinafter referred to as print sections 12Y to 12K) that are sequentially transferred and superimposed on the paper P are sequentially arranged from the upstream side in the transport direction.

  A paper transport unit 14 that transports the continuous paper P to the print units 12Y to 12K is provided on the upstream side in the transport direction of the print units 12Y to 12K. Further, on the downstream side in the transport direction of the printing units 12Y to 12K, the fixing unit 16 that fixes the unfixed toner image transferred by the printing units 12Y to 12K to the continuous paper P, and the continuous paper P that has passed through the fixing unit 16 are discharged. A paper discharge unit 17 for paper is provided.

  In the following, when it is necessary to distinguish Y, M, C, and K, description is given by adding any of Y, M, C, and K after the reference numeral, and Y, M, C, and K are distinguished. If there is no need to do this, Y, M, C, and K are omitted.

  The paper transport unit 14 includes a main drive roll 18 around which the continuous paper P is wound. The main drive roll 18 is driven by a paper transport motor (not shown), which is a stepping motor, and a controller 70 (see FIG. 3) that controls the entire printer 10 controls the continuous paper P based on the number of pulses of the paper transport motor. Control the feed amount.

  Further, as shown in FIG. 1, idle rolls 19 </ b> A and 19 </ b> B around which continuous paper P is wound are provided on the upstream side in the transport direction of the main drive roll 18 of the paper transport unit 14. An idle roll 19C around which the continuous paper P is wound is disposed on the downstream side. Further, the idle roll 19D is in pressure contact with the main drive roll 18. The idle roll 19D and the main drive roll 18 sandwich and convey the continuous paper P.

  A transport guide 26 and an aligning roll 27 are disposed between the idle roll 19A and the idle roll 19B. The conveyance guide 26 is formed with a U-shaped curved surface around which the continuous paper P is wound and a side guide (not shown) that guides one end of the continuous paper P in the width direction (a direction orthogonal to the conveyance direction). Yes.

  The aligning roll 27 is a roll whose roll width is narrower at each stage than the idle rolls 19A, 19B, 19C, and 19D, and whose rotation axis is obliquely intersected with the conveyance direction of the continuous paper P. The continuous paper P is brought close to one end in the width direction by coming into contact with one end in the width direction. As a result, one end of the continuous paper P in the width direction is abutted against the guide rib of the conveyance guide 26, and the skew of the continuous paper P is corrected.

  The main drive roll 18, idle rolls 19A, 19B, 19C, and 19D, the paper transport motor, the transport guide 26, and the aligning roll 27 are supported by the paper transport frame 21 directly or via a support member. The paper transport frame 21 is supported by the base 23.

  Each of the printing units 12Y to 12K includes a photoconductor 22, and a transfer roll 24, a cleaning device 28, a charging charger 30 and a print are sequentially arranged around the photoconductor 22 in the rotation direction of the photoconductor 22 (in the direction of the arrow in the drawing). A head 32 and a developing device 34 are provided. The printing units 12Y to 12K include print frames 38Y to 38K that support the photosensitive member 22, the cleaning device 28, the charging charger 30, and the print head 32, respectively. Adjacent print frames 38Y to 38K are connected by connecting bases 54 that support the print frames 38Y to 38K so as to be movable up and down with bolts and nuts (both not shown), and connect the print frames 38Y to 38K to each other. This is done by positioning and screwing through a plate (not shown). Further, the base 54 that supports the print frame 38 </ b> Y is connected to the base 23 that supports the paper transport frame 21.

  In each printing unit 12, the charging charger 30 uniformly charges the surface of the photosensitive member 22 to a predetermined potential, and the print head 32 exposes the surface of the photosensitive member 22 charged by the charging charger 30 along the main scanning line (line exposure). ) To form a latent image.

  FIG. 2A is a diagram illustrating a schematic configuration of the print head 32, and FIG. 2B is a diagram illustrating an exposure image by the print head 32.

  Each color print head 32 includes an LED array 80 in which a plurality of LEDs 80a are arranged in the main scanning direction, and a SELFOC lens array (SLA) 88 is provided on the light emission side of the LED array 80. Light emitted from the LED array 80 is applied to the photosensitive member 22 via the SLA 88. In the present embodiment, an LED is applied as the light-emitting element of the present invention. However, the present invention is not limited to this, and other light-emitting elements such as an EL (Electro-Luminescence) element may be applied. Further, the array in the main scanning direction of the LED array 80 may be two or more rows in addition to one row, or may be partially staggered.

  The LED array 80 is driven via a driver IC 84 by a print head driving unit described later. The LED array 80 and the driver IC 84 are disposed on the printed circuit board 86, and the print head 32 has a long shape in the main scanning direction as a whole.

  Further, on the printed circuit board 86, data relating to the recording position in the sub-scanning direction of dots recorded by the respective LEDs 80a of the LED array 80 measured at the time of manufacturing the print head 32 (for example, dot position deviation in the sub-scanning direction with respect to the design value) A storage unit 82 for storing data indicating the amount) is provided.

  The developing device 34 includes three developing magnet rolls arranged along the axial direction of the photosensitive member 22, and a conveying magnet roll that conveys a two-component toner composed of toner and a carrier to the three developing magnet rolls. The toner and carrier charged in the developing cartridge are agitated and charged, and are equipped with two agitating screws that mix evenly. The toner adheres to the latent image formed on the photosensitive member 22 and is thus provided. Form an image.

  The transfer roll 24 abuts on the upper surface of the photosensitive member 22, and sandwiches and conveys the continuous paper P together with the photosensitive member 22. At this time, the toner image formed on the photosensitive member 22 is transferred to the continuous paper P by the developing device 34. . Two guide rolls 40 are provided on the upstream side and the downstream side in the transport direction of the transfer roll 24. The guide roll 40 moves up and down at a suitable timing according to the transfer operation.

  The cleaning device 28 scrapes off and removes untransferred residual toner remaining on the surface of the photosensitive member 22 without being transferred to the continuous paper P.

  The fixing unit 16 includes a flash fixing device 52, idle rolls 54 </ b> A, 54 </ b> B, 54 </ b> C, and a paper discharge roll 56. The idle rolls 54A, 54B, 54C, the flash fixing device 52, and the paper discharge roll 56 are arranged in this order in the transport direction, and these are supported by the fixing frame 58 at both ends in the direction orthogonal to the transport direction. Yes.

  The idle rolls 54A, 54B, and 54C are disposed on the back side of the printing surface of the continuous paper P, and the idle roll 54C is disposed above the idle roll 54B. For this reason, the continuous paper P wound around the idle rolls 54A, 54B, 54C is reversed and conveyed with the printing surface facing upward.

  The flash fixing device 52 is disposed on the printing surface side of the continuous paper P conveyed with the printing surface facing upward, and irradiates the printing surface of the continuous paper P with infrared rays. As a result, the unfixed toner on the continuous paper P is heated and melted, and then solidified and fixed on the continuous paper P.

  The paper discharge roll 56 discharges the toner-fixed area of the continuous paper P from the printer 10, but the continuous paper P that has passed through the flash fixing device 52 is once discharged from the fixing unit 16 and passed through the paper discharge unit 17. After passing, the paper returns to the fixing unit 16 and is discharged by the paper discharge roll 56.

  Further, the fixing unit 16 includes a misregistration amount detection sensor 90 that detects misregistration amounts of C, M, Y, and K colors. Two misregistration amount detection sensors 90 are provided along the paper conveyance path, at the start position of writing by the print head 32 and the end position of writing, that is, near both ends in the main scanning direction (paper width direction of the continuous paper P). Then, the registration marks (small marks for detecting the misregistration amounts of the respective colors Y, M, C, and K) recorded at both ends in the width direction of the continuous paper P are read to detect the misregistration amounts of the respective colors.

  In the paper discharge unit 17, an idle roll 59A, a tension applying roll 60, a sub drive roll 61, an idle roll 59B, a transport guide 62, an aligning roll 63, and an idle roll 59C are arranged in this order in the transport direction. Are supported by the paper discharge frame 65 directly or via a support member at both ends in a direction orthogonal to the transport direction. The paper discharge frame 65 is connected to the print frame 38K and the fixing frame 58.

  The sub drive roll 61 is disposed above the idle roll 59A, and the continuous paper P wound around the idle roll 59A and the sub drive roll 61 is redirected and conveyed upward. The idle roll 59 </ b> B is in pressure contact with the sub drive roll 61, rotates following the rotation of the sub drive roll 61, and sandwiches and conveys the continuous paper P together with the sub drive roll 61.

  Further, a tension applying roll 60 is disposed between the idle roll 59A and the sub drive roll 61, and the continuous paper P is between the idle roll 59A and the tension applying roll 60, and between the tension applying roll 60 and the sub drive roll. It is meandering between 61 and being conveyed.

  The tension applying roll 60 is supported at both ends in the axial direction so as to be swingable by arms (not shown). The arm is biased toward the continuous paper P by a biasing means (not shown) such as a spring, and the tension applying roll 60 is biased toward the continuous paper P. As a result, tension is applied to the continuous paper P.

  Further, the position of the arm is detected by a sensor (not shown), and the rotation speed of the sub drive roll 61 is controlled so that the position of the arm is always located at a fixed position.

  Further, a transport guide 62 and an aligning roll 63 are disposed downstream of the sub drive roll 61 in the transport direction. The conveyance guide 62 and the aligning roll 63 have the same configuration as the conveyance guide 26 and the aligning roll 27 disposed in the paper conveyance unit 14 and correct the skew of the continuous paper P.

  An idle roll 59 </ b> C is disposed downstream of the conveyance guide 62 in the conveyance direction. The continuous paper P is wound around the idle roll 59 </ b> C, and the direction is changed toward the paper discharge roll 56 of the fixing unit 16.

  FIG. 3 is a block diagram showing a schematic configuration of a control system for driving the print head 32.

  As shown in FIG. 3, the printer 10 is provided with a controller 70. The controller 70 includes a microcomputer including a CPU, a ROM, a RAM, and the like, and controls the entire printer 10. A print head driving unit 72 is connected to the controller 70.

  The print head driving unit 72 is connected to the print head 32 for each color and the skew correction motor 74 and the side registration actuator 75 provided corresponding to each print head.

  As described above, the print head 32 for each color includes the LED array 80 and the storage unit 82.

  The light emission of the LEDs 80 a constituting the LED array 80 is controlled by the print head driving unit 72. The print head drive unit 72 controls light emission of the LEDs 80a of the LED array 80 based on image data input from the controller. A latent image is formed on the photosensitive member 22 by light emission of each LED 80a.

  In the storage unit 82, as described above, data relating to the recording position in the sub-scanning direction of the dots recorded by each LED 80a of the LED array 80 measured at the time of manufacturing the print head 32 (for example, the dot in the sub-scanning direction with respect to the design value) Data indicating the amount of misalignment) is stored. Based on the data stored in the storage unit 82, the light emission timing of the LED array 80 (LED 80a) of each print head is controlled.

  4 and 5 are diagrams illustrating examples of data stored in the storage unit 82 of a predetermined print head 32 serving as a reference and the storage unit 82 of another print head 32 serving as a correction target.

  In FIG. 4, a predetermined print head serving as a reference is a print head 32K that forms an electrostatic latent image corresponding to a K toner image, and another print head to be corrected is an electrostatic corresponding to a Y toner image. The print head 32Y forms a latent image. In FIG. 5, a predetermined print head serving as a reference is a print head 32K that forms an electrostatic latent image corresponding to a K toner image, and the other print heads to be corrected are static prints corresponding to an M toner image. Assume that the print head 32M forms an electrostatic latent image.

In FIG. 4A, the positional deviation amount with respect to the design value (the positional deviation amount E _S = 0) along the sub-scanning direction of each dot recorded on the photosensitive member 22K by each LED 80a in the print head 32K is indicated by a solid line. In addition, the broken line indicates the amount of positional deviation with respect to the design value along the sub-scanning direction of each dot recorded on the photosensitive member 22Y by each LED 80a in the print head 32Y. In FIG. 4B, a solid line indicates a positional deviation amount with respect to a design value (a positional deviation amount E _M = 0) along the main scanning direction of each dot recorded on the photosensitive member 22K by each LED 80a in the print head 32K. In addition, a broken line indicates a positional deviation amount with respect to a design value along the main scanning direction of each dot recorded on the photosensitive member 22Y by each LED 80a in the print head 32Y.

On the other hand, FIG. 5A shows a positional deviation amount with respect to a design value (a positional deviation amount E _S = 0) along the sub-scanning direction of each dot recorded on the photosensitive member 22K by each LED 80a in the print head 32K by a solid line. In addition, a broken line indicates a positional deviation amount with respect to a design value along the sub-scanning direction of each dot recorded on the photosensitive member 22M by each LED 80a in the print head 32M. In FIG. 5B, the positional deviation amount with respect to the design value (the positional deviation amount E _M = 0) along the main scanning direction of each dot recorded on the photosensitive member 22K by each LED 80a in the print head 32K is indicated by a solid line. In addition, a broken line indicates a positional deviation amount with respect to a design value along the main scanning direction of each dot recorded on the photosensitive member 22M by each LED 80a in the print head 32M.

4 and FIG. 5 shows an area where an electrostatic latent image is formed on the photoconductor 22 along the main scanning direction, and each print head 32 is located in the image forming area _WIM . An electrostatic latent image is formed on the photoreceptor 22 using the corresponding LED 80a. Here, the image forming region W _IM in Figure 4, the photosensitive member 22 along the main scanning direction shows the case of forming an electrostatic latent image of maximum width (full-size), and imaged region W _IM in FIG. 5 Shows a case where an electrostatic latent image of about ½ size of the full size is formed on the photoconductor 22 along the main scanning direction.

In the color printer 10, when image data corresponding to an output image is input from an information processing apparatus outside the apparatus such as a host computer to the print head driving unit 72 via the controller 70, the image data is transferred to the print head driving unit 72 by Y, The image data IM _Y to _K corresponding to the M, C, and K toner images are converted into the image data IM _Y to _K , respectively, and the image data IM _Y to _K are respectively sent to the LED array 80 of the print heads 32Y, 32M, 32C, and 32K at a predetermined timing. Is output. The LED array 80 of the print heads 32Y, 32M, 32C, and 32K that has received the image data IM _Y to _K causes the LED 80A to emit light in synchronism with the video clock to generate an electrostatic latent image on the photosensitive member 22 that rotates in the sub-scanning direction. Form.

  The print head driving unit 72 executes initial registration correction for the print heads 32Y, 32M, 32C, 32K, at least immediately after the power is turned on and before the start of image formation with a size different from the previous image formation. . The initial registration adjustment by the print head driving unit 72 will be described with reference to the flowchart of FIG.

In step 100, the print head driving unit 72 each printhead 32Y, M, C, positional displacement amount along the positional deviation amount E _S and the main scanning direction along the sub-scanning direction for all LED80A from the storage unit 82 of the K E _M and the positional deviation amount E _S are read out.

In step 102, the print head driving unit 72 determines the range of the image forming area W _IM in which the electrostatic latent image is formed based on the image data IM _Y to _K , and the image forming area is determined from all the LEDs 80A in each print head 32. The LED 80A used for forming an image on the IM is selected, and only the data corresponding to the LED 80A used for image formation (the positional deviation amount E _S ) is extracted from the positional deviation amount E _S for all the LEDs 80A. .

In step 104, read the print head driving unit 72, except for the print head 32K serving as a reference on the basis of the positional deviation amount E _S extracted in step 102, other print heads 32Y, M, along the main scanning direction with respect to C registration correction amount R _LR and skew correction amount R _SC calculates respectively.

At this time, the print head driving unit 72 for the dots to be recorded in the image forming area W _IM by LED80A a predetermined range in the print head 32K, the print head 32Y, M, imaging regions by LED80A a predetermined range in the C W _IM The lead registration correction amount R _LR and the skew correction amount R _SC are calculated so that the sum of squares of the respective positional deviation amounts along the sub-scanning direction of the dots recorded in the respective cases is minimized.

In step 106, the print head driving unit 72 determines the range of the image forming area W _IM in which the electrostatic latent image is formed based on the image data IM _Y to _K , and the image forming area is determined from all the LEDs 80A in each print head 32. The LED 80A used for forming an image on the IM is selected, and only the data corresponding to the LED 80A used for image formation (the positional deviation amount E _M ) is extracted from the positional deviation amount E _M for all the LEDs 80A. .

In step 108, the print head driving unit 72 removes the reference print head 32K based on the misregistration amount E _M extracted in step 102, and the side along the main scanning direction with respect to the other print heads 32Y, 32M, 32C. The resist correction amount R _SD is calculated.

At this time, the print head driving unit 72 for the dots to be recorded in the image forming area W _IM by LED80A a predetermined range in the print head 32K, the print head 32Y, M, imaging regions by LED80A a predetermined range in the C W _IM The side registration correction amount _RSD is calculated so that the sum of squares of the respective positional deviation amounts along the main scanning direction of each dot recorded in each of the dots is minimized.

In step 110, the print head drive unit 72 outputs a drive signal _DSc (see FIG. 3) corresponding to the skew correction amount R _S calculated in step 104 to each skew correction motor 74 in the print heads 32Y, 32M, 32C. . As a result, each of the Y, M, and C skew correction motors 74 causes the LED array 80 in the print heads 32Y, 32M, and 32C to have a skew correction amount R _S on the other end side with one end portion in the main scanning direction as a rotation center. Rotate (forward or reverse) by the corresponding amount of rotation.

In step 112, the print head driving unit 72 outputs the drive signal D _SD (see FIG. 3) corresponding to the side registration correction amount R _SD calculated in step 108 to each of the side registration actuators 75Y, 75Y in the print heads 32Y, M, C. Output to M and C. Thus, Y, M, each side resist actuator 75Y of C, M, C, the print head 32Y, M, by a distance corresponding to the side registration correction amount R _SD along the LED array 80 in the main scanning direction in the C Move (forward or backward).

In step 114, the print head driving unit 72 outputs the image data IM _Y to _K to each LED array 80 of the print heads 32Y, 32M, 32C, as many as the number of clocks corresponding to the read registration correction amount R _LR calculated in step 104. The output timing of each image data IM _Y to _K is set so as to change the timing (delay or forward). As a result, the light emission timing by the LED array 80 of the print heads 32Y, 32M, 32C changes (delays or forwards) with respect to the light emission timing by the print head 32K corresponding to the lead registration correction amount _RLR .

  Next, the relationship between the image size and the correction target LED 80A will be described with reference to FIGS. When forming the toner image having the full-size image forming area IM shown in FIG. 5, N LEDs 80A in the LED array 80 are used, and the (N + 1) LEDs 80A are respectively moved from the writing position to the writing end position. The identification numbers “1” to “N” are assigned in order. Here, for convenience, N is an even number.

Therefore, when forming a toner image having the full-size image forming area IM, read registration correction and skew correction for the print heads 32Y, 32M, 32C are performed from “No. 1” to “#” in the print heads 32Y, 32M, 32C. Deviations δ _{S1 to} δ _{SN in} the sub-scanning direction between the dots recorded by the N-th LED 80A and the dots recorded by the “1st” to “N-th” LED 80A in the print head 32K (FIG. 4A) Reference) The read resist correction amount R _LR and the skew correction amount R for each of the print heads 32Y, 32M, and 32C are obtained by the print head driving unit 72 so that the square sum of these δ _S1 to δ _SN is minimized. _SC is calculated.

Further, the side registration correction for the print heads 32Y, 32M, 32C is performed by the dots recorded by the LED 80A of No. 0 to No. N in the print heads 32Y, 32M, 32C and the No. 1 to No. N in the print head 32K. The deviations δ _{M1 to} δ _{MN in} the main scanning direction from the dots recorded by the LED 80A are obtained (see FIG. 4B), respectively, so that the square sum of these δ _M1 to δ ^MN is minimized. The side registration correction amount R _SD is calculated for each of the print heads 32Y, 32M, and 32C by the print head driving unit 72.

On the other hand, when a toner image having a half-size image forming area IM is formed, the read resist correction and skew correction for the print heads 32Y, 32M, 32C are “N / 2” in the print heads 32Y, 32M, 32C. Deviation δ _{S (N / 2) in} the sub-scanning direction between the dot recorded by the “N” LED 80A and the dot recorded by the “N / 2” to “N” LED 80A in the print head 32K δ _SN are respectively obtained (see FIG. 5A), and the print head driving unit 72 causes the print heads 32Y, M, and C to have a minimum sum of squares of δS _{(N / 2) to} δ _SN . For each, a lead resist correction amount _RLR and a skew correction amount _RSC are calculated.

In addition, the side registration correction for the print heads 32Y, 32M, 32C is performed using dots ("N / 2") to "N" LED 80A in the print heads 32Y, 32M, 32C and "(N / 2) Deviations δ _{S (N / 2)} ˜δ _{SN in} the main scanning direction from the dots recorded by the LEDs 80A of No. “No.” to “N” (see FIG. 5B) are obtained respectively. as the sum of squares of _{S (N / 2) ~δ SN} is minimized, the print head 32Y by the print head driving unit 72, M, side registration correction amount R _SD is calculated for each of the C.

  The initial registration correction described above has been described as being performed immediately after the power is turned on and before the start of image formation and before the start of image formation of a different size from the previous image formation. It may be performed when an initial registration correction command is input to the controller 70 or whenever a predetermined number of images of the same size are formed.

  In the initial registration correction, lead registration correction, skew correction, and side registration correction are performed on the Y, M, and C print heads 32Y, M, and C with reference to the K print head 32K. The lead registration correction, skew correction, and side registration correction for the other print heads 32 may be executed with the head 32 as a reference.

In the color printer 10 according to the present embodiment described above, the print head driving unit 72 uses other LEDs 80A in the reference print head 32K for other dots recorded in the image forming area W _IM of the photoreceptor 22K. comprising printhead 32Y, M, photoreceptor 22Y by each LED80A in C, M, and the square sum of the positional displacement amount along the sub-scanning direction of the dots that are recorded respectively in the imaged region W _IM of C minimum As described above, the lead registration correction amount R _LR and the skew correction amount R _SC along the main scanning direction for the other print heads 32Y, 32M, 32C are calculated.

In this case, the width of the image forming region W _IM (image size of the output image) is changed, the arrangement each printhead 32Y, M, C, is LED80A used to form a monochrome image in K along the main scanning direction However, in the color printer 10 according to the present embodiment, the print head driving unit 72 uses the LED 80A corresponding to the image forming area W _IM among all the LEDs 80A in the print heads 32Y, 32M, 32C, and 32K. since the correction data when only the position of the dot to calculate the read registration correction amount R _LR and skew correction amount R _SC formed by the image size of an output image be varied, always depending on the image size it calculates the optimum read registration correction amount R _LR and skew correction amount R _SC.

Then, the color printer 10 according to the present embodiment, the print head driving unit 72 is read registration correction amount R _LR other print heads 32Y based on, M, while changing the light emission timing of LED80A in C, the skew correction amount R By changing the amount of inclination of the other print heads 32Y, 32M, 32C with respect to the main scanning direction based on the _SC , other dots for each dot recorded on the photosensitive member 22K by the respective LEDs 80A in the reference print head 32K. The respective misregistration amounts along the sub-scanning direction of the dots recorded on the photosensitive members 22Y, M, and C by the LEDs 80A in the print heads 32Y, M, and C are used to form an electrostatic latent image. Can be minimized as the average of the entire plurality of LEDs 80A. Displacement (color misregistration) along the main scanning direction of other single color images (Y, M, C) with respect to the predetermined single color image (K) to be visually inconspicuous. I can.

  As a result, according to the color printer 10 according to the present embodiment, for example, the LEDs 80 </ b> A arranged at a part along the main scanning direction of the print head 32 such as both ends and the center along the main scanning direction of the print head 32. The lead registration correction amount and the skew correction amount are set based on only the dots recorded by the above, and the reference in the output image is compared with the case where the print head is subjected to the lead registration correction and the skew correction according to the lead registration correction amount and the skew correction amount. Therefore, it is possible to effectively improve the image quality deterioration due to the positional shift (color shift) along the sub-scanning direction of the other single-color image (Y, M, C) with respect to the predetermined single-color image (K).

Further, in the color printer 10 according to the present embodiment, the print head drive unit 72 uses the other print heads 32Y, 32M, 32C for each dot recorded on the photoreceptor 22K by each LED 80A of the reference print head 32K. Each LED 80A is aligned along the main scanning direction with respect to the other recording heads so that the sum of squares of the positional deviation amounts along the main scanning direction of each dot recorded on the photosensitive members 22Y, 22M, 22C is minimized. The side registration correction amount R _SD is calculated.

At this time, when the width of the image forming area W _IM (image size of the output image) changes, the range in which the LEDs 80A used for forming a single color image in each print head 32 are arranged along the main scanning direction also changes. but the color printer 10 according to the present embodiment, the print head driving unit 72, among all LED80A in the print head 32, only the position of the dot side registration correction which is formed by an LED corresponding to the image forming region W _IM Since the correction data for calculating the amount R _SD is used, the optimum side registration correction amount R _SD corresponding to the image size can always be obtained even if the image size of the output image changes.

Then, the color printer 10 according to the present embodiment, the print head driving unit 72, the side registration correction amount other print heads 32Y based on R _SD, M, by displacing along the main scanning direction C, the reference For each dot recorded on the photoreceptor 22K by each LED 80A in the print head 32K, the main of each dot recorded on the photoreceptor 22Y, M, C by each LED 80A in the other print head 32Y, M, C. Since each displacement amount along the scanning direction can be minimized as an average of the whole of a plurality of light emitting elements used for forming an image, other monochrome image with respect to a predetermined monochrome image serving as a reference in the output image can be reduced. Misalignment (color misregistration) along the main scanning direction is visually inconspicuous by dispersing along the main scanning direction. Can Rukoto.

  As a result, according to the color printer 10 according to the present embodiment, for example, the side registration correction amount is set based on only dots recorded by the LEDs arranged at both ends of the print head in the main scanning direction. Compared to the case where the recording head is subjected to side registration correction according to the correction amount, the positional deviation in the main scanning direction of other monochrome images (Y, M, C) with respect to a predetermined monochrome image (K) serving as a reference in the output image ( It is possible to effectively improve image quality degradation caused by color misregistration.

  In the color printer 10 according to the present embodiment, an example in which the storage unit 82 that stores data related to dot recording positions is provided in each print head 32 has been described. However, the present invention is not limited to this. Is stored in the printer 10 or in an external device capable of mutually transmitting and receiving data, and the serial number of the print head 32 is set. The print head driving unit 72 may read out and read out corresponding data from the storage unit.

1 is a side view illustrating a schematic configuration of a color printer according to an embodiment of the present invention. (A) is a diagram showing a schematic configuration of the print head 32, and (B) is a diagram showing an exposure image by the print head 32. FIG. It is a block diagram which shows schematic structure of the control system for driving a print head. It is a figure which shows an example of the data respectively stored in the memory | storage part 82 of the predetermined print head 32K used as a reference | standard, and the memory | storage part 82Y of the other print head 32 used as correction | amendment object. It is a figure which shows an example of the data respectively stored in the memory | storage part 82 of the predetermined | prescribed print head 32K used as a reference | standard, and the memory | storage part 82M of the other print head 32 used as correction | amendment object. 6 is a flowchart illustrating a flow of initial registration correction processing performed in a print head driving unit.

Explanation of symbols

10 Color printer 22Y, M, C, K Photosensitive member (image carrier)
32Y, M, C, K Print head (recording head)
70 controller 72 print head drive section (first and second correction amount calculation means, lead registration correction means, skew correction means, side registration correction means)
74Y, M, C, K Skew correction motor (skew correction means)
75Y, M, C, K Side registration actuator (side registration correction means)
80 LED array 80A LED
82 storage unit (first and second storage means)

Claims (7)

A plurality of recording heads each having a plurality of output elements arranged in a line are provided along the movement path of the image carrier, and a single color image formed by each recording head is superimposed on the image carrier that moves in the sub-scanning direction. An image forming apparatus for forming an output image of a plurality of colors by
For each dot recorded in the image forming area of the image carrier by each output element in the predetermined recording head as a reference, each output element in the other recording head in the image forming area of the image carrier. The lead registration correction amount along the main scanning direction with respect to the other recording head and the main scanning with respect to the other recording head so that the positional deviation amount of each dot to be recorded along the sub-scanning direction is minimized. First correction amount calculating means for calculating a skew correction amount with respect to the direction;
Lead registration correction means for changing the output timing of the output element in the other recording head based on the read registration correction amount calculated by the first correction amount calculation means;
Skew correcting means for changing an inclination amount of the other recording head with respect to the main scanning direction based on the skew correction amount calculated by the first correction amount calculating means;
An image forming apparatus comprising: For each dot recorded in the image forming area of the image carrier by each output element in the predetermined recording head as a reference, each output element in the other recording head in the image forming area of the image carrier. Second correction amount calculation for calculating a side registration correction amount along the main scanning direction with respect to the other recording head so that a positional deviation amount of each dot to be recorded along the main scanning direction is minimized. Means,
Side registration correction means for displacing the other recording head along the main scanning direction based on the side registration correction amount calculated by the second correction amount calculation means;
The image forming apparatus according to claim 1, further comprising: The image forming apparatus according to claim 1, wherein the correction amount calculation unit calculates a correction amount that minimizes a sum of squares of the respective displacement amounts. The recording head has first storage means for storing relative positional relationships along the main scanning direction of dots respectively recorded on the image carrier by all output elements provided in the recording head. And
The first correction amount calculating means is recorded on the image carrier by each output element corresponding to the image forming area among all output elements in the recording head stored in the first storage means. 4. The read resist correction amount and the skew correction amount for the other recording head are determined based on a relative positional relationship of each dot along the main scanning direction. The image forming apparatus according to claim 1. The recording head includes second storage means for storing a relative positional relationship along the sub-scanning direction of each dot recorded on the image carrier by all output elements provided in the recording head. Have
The second correction amount calculation means is recorded on the image carrier by each output element corresponding to the image forming area among all output elements in the recording head stored in the second storage means. 5. The side registration correction amount with respect to the other recording head is determined based on a relative positional relationship of each dot along the sub-scanning direction. 6. Image forming apparatus.   6. The image forming apparatus according to claim 1, wherein a correction operation is performed when an image having a size different from that at the previous image formation is performed.   The recording head has a light emitting element as an output element. By exposing a photosensitive member provided opposite to the recording head from the light emitting element, an output image is formed along the main scanning direction of the image carrier. 7. The image forming apparatus according to claim 1, wherein dots are recorded by electrophotography in an image forming area having a corresponding width.

Images